The study will consist of two parts: a dose-escalation part (Part 1) and a dose expansion part (Part 2). In both study parts, SSGJ-705 will be administered，the administration duration may be adjusted based on outcomes of previous patients if necessary) followed by safety, PK, PD, potential anti tumor effects and immunogenicity evaluation.

Inclusion Criteria:

• ≥18 year, male or female.
• Life expectancy ≥12 weeks (according to Investigator's judgement).
• Patients with histologically or cytologically confirmed locally advanced or metastatic non resectable HER2-expressing Solid Tumors
• Patients who have at least one measurable lesion (radiation-naïve) according to RECIST v1.1
• ECOG performance status 0-1
• Adequate organ and bone marrow function evaluated by laboratory tests
• Male patients who are surgically sterilized or who agree to use highly effective contraceptive measures during the study and for at least 6 months after administration of the last study drug dose
• Willing to provide written informed consent and willing and able to comply with all study procedures.

Exclusion Criteria:

• Receive chemotherapy, targeted therapy, or other antitumor therapy within 3 weeks prior to initial dosing
• Patients whose toxicity due to previous anticancer therapy has not been reduced to NCI CTCAE Grade 1 or lower, or any greater than NCI CTCAE 1 AE exists within 2 weeks before enrollment, not including hair loss and fatigue
• Patients requiring systemic systemic therapy with systemic hormones or other immunosuppressive agents within 4 weeks prior to initial administration and during the study period
• Previous cumulative doses of adriamycin > 720 mg/m2, adriamycin >360 mg/m2 or other cumulative doses of adriamycin were converted to equal doses of adriamycin >360 mg/m2
• Patients who underwent major surgery within 4 weeks of initial dosing and have not fully recovered or who plan to undergo major surgery during the trial
• In addition to palliative radiotherapy, other anticancer treatments not specified in the protocol are planned for the duration of the trial
• Always received total pelvic radiotherapy
• Had an active or prior autoimmune or inflammatory disease within the last 3 years prior to study treatment
• Severe disease of cardiovascular and cerebrovascular diseases
• History of active tuberculosis
• A history of (non-infectious) pneumonia/interstitial pneumonia or a history of present pneumonia/interstitial pneumonia requiring steroid treatment
• Severe dyspnea or the need for supplemental oxygen therapy at rest due to complications of advanced malignancy; Newly diagnosed or symptomatic central nervous system (CNS) metastasis, spinal cord compression, or cancerous meningitis
• Persons with a history of primary immunodeficiency disease, including but not limited to HIV-positive serum
• Hepatitis B virus (HBV) and hepatitis C virus (HCV) positive subjects
• Women/men who are pregnant or breast-feeding or planning to give birth
• A history of mental or substance abuse that may affect study compliance
• Allergy to other antibody drugs or to any excipients in the study drug
• Who received live vaccine within 30 days prior to initial administration (within 72 hours for COVID-19 vaccine), or who plan to receive any live vaccine during the study
• Previous organ and allogeneic stem cell transplants (except transplants that do not require immunosuppressive therapy, such as corneal and hair transplants)
• Participated in any medical device or drug clinical study within 1 month prior to screening
• The inestigators considered that this would significantly increase the risk of administration of the investigational drug, or that it would affect efficacy evaluation or other conditions requiring exclusion